Abstract: A valve body is disclosed located in the hydraulic system of a machine which valve serves to direct hydraulic fluid under pressure to hydraulic components or divert the fluid to a system reservoir to prevent component operation. A check valve in the valve body is opened or closed by control means with the check valve indirectly determining the position of a pressure responsive spool for either normal fluid passage to hydraulic components or fluid diversion back to a reservoir. Remote actuation of the control means is by a hand operated air, lockable pump to enable an authorized equipment operator to remotely actuate said control means to effect locking or unlocking of the hydraulic system by positioning the check valve. A modified check valve control dispenses with the air pump and utilizes a lock plunger to bias the check valve to a closed position for normal hydraulic system operation or, conversely, to open the check valve to divert pressurized fluid back to a system reservoir.